The invention relates generally to electron beam ion sources (EBIS), and particularly to an apparatus including a refrigerated electron beam ion trap (EBIT) system which preferably reduces reliance on liquid gases for cooling.
An electron beam ion trap (EBIT) is a spin-off development of an electron beam ion source (EBIS). The basic physical principle behind EBIT or EBIS is the trapping of low charge state ions in the space charge potential of the compressed electron beam and the subsequent successive ionization, which produces very highly charged ions depending in range on the electron beam ionization energy. The electron beam is compressed in a coaxial magnetic field (xcx9c3 Tesla) of a super-conducting magnet. The first operational EBIS was demonstrated in 1967, and the operation of an EBIT as a source was first reported in 1990. In these prior devices, the extracted ion species and charges range from H+ to Th80+ with energies variable between 2 keV to 30 keV per charge. A description of prior electron beam ion sources incorporating an ion trap may be found in Schneider et al., xe2x80x9cIon collision experiments with slow, very highly charged ions extracted from an electron-beam ion trapxe2x80x9d Phys. Rev. A 42, 3889 (1990), which is incorporated herein by reference for this purpose.
Generally, prior art electron beam ion traps and sources require liquid, cryogenic cooling gases (typically helium and nitrogen) to maintain operational conditions. In these prior art sources and traps, a liquid nitrogen vessel forms the outer cold shield that cools the interior of the vacuum vessel from ambient temperature to prevent significant cook-off of liquid helium. Additionally an inner, liquid helium-filled vessel surrounds the ultra-high vacuum trap core including super-conducting compression magnets. The prohibitive cost of liquid helium is a driving factor in reducing the range of application of such sources of highly charged ions.
In accordance with a preferred embodiment, an electron beam device is provided for producing ions. The device includes an electron beam source configured to produce an electron beam and a trap core inline with the electron beam. A compression magnet is located in the trap core and is configured to compress the electron beam and a first cooling contact in thermal communication with the trap core. A refrigerator system is provided which cools the trap core by cooling the cooling contact, with a first thermally conductive, solid link located between the first cooling contact and the refrigerator system. The device also includes a collection magnet inline with the electron beam, the collection magnet being located downstream of the compression magnet. An outer cold shield substantially surrounds the electron beam source, trap core, and collection magnet.
In accordance with another preferred embodiment, a refrigeration system for maintaining cryogenic conditions at the core of an electron beam ion trap is provided. The refrigeration system includes a cryo-refrigerator configured to cool a trap core and a cold shield that separates a substantially room-temperature trap exterior from the trap interior. In addition, a first cryo-head is in solid thermal communication with the trap core is provided, with a compression magnet being located within the trap core. A first thermally conductive solid link is also provided between the cryo-head and the cryo-refrigerator.
In accordance with yet another preferred embodiment, a method of cooling a trap core of an electron beam device for producing ions is provided. The method includes the steps of producing an electron beam and compressing the electron beam in the trap core using a compression magnet. The trap core is cooled by predominantly conductively transferring heat produced in the trap core to a first cooling contact. This heat is conducted from the cooling contacts through a first solid thermally conductive link to a first cryo-refrigerator. A resulting ion beam is then outputted.
As a result of the features described herein, preferred embodiments of the present invention are preferably capable of functioning like a typical electron beam ion trap, while at the same time offering the advantages of greatly reduced size and cost. For example, the elimination of the liquid gas based refrigeration system, especially the liquid helium cooling component of the system, reduces the operation cost of the trap-source, which is traditionally dominated by the cost of liquid helium in the prior art. As a result, new applications of electron beam ion trap-sources are made possible in a wide variety of fields, such as semi-conductor manufacturing to biomolecular fragmentation, among others. In addition, preferred embodiments of the present invention are able to operate at low electronic beam energies which, in turn, allows production of low energy ion beams.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the invention having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.